Rack-and-pinion steering devices typically employ a pinion that drives a rack with meshed gear teeth. The pinion provides the steering input. Links coupled at the ends of the rack provide the steering output. Typically the pinion is coupled to a steering shaft and steering wheel. The ends of the rack are coupled to right and left tie rod assemblies and wheels. This standard system relies on the ends of the rack for pushing and pulling the tie rods when the rack moves laterally by virtue of rotating the steering wheel, the steering shaft, and the pinion. In the standard steering system, the rack acts as a structural member; this may cause problems with adequate support and strength of the system, leading to fatigue or failure. It may also cause misalignment of the tie rods with the suspension system, creating inadvertent steering action during suspension travel.
Typical rack-and-pinion systems further create the problem of an undesirable angle of the tie rods coupled to the wheels because the tie rods are coupled at or beyond the ends of the rack. This can result in a steep angle of the tie rods as coupled to the wheel. This can also increase the stress on the components of the tie rod assemblies and on the steering system when turning or when driving over uneven surfaces. This undesirable angle may be the result of the steering output being coupled to the tie rods at a position relatively far away from the steering input and from the rack itself.
Another problem of the common rack-and-pinion systems concerns the amount of space required to achieve the results of the system described above. Providing a lengthy rack coupled to tie rods beyond the ends of the rack requires a steering system that can comprise much lateral space, leaving little space for tie rod assemblies with desirable configurations. It may also leave little room for suspension components. This poses problems for smaller vehicles and vehicles that require additional structural support members, such as recreational off-road vehicles.
Yet another concern relates to the undesirable angles that result from including a typical rack-and-pinion steering system described above. Providing tie rod couplings positioned outside of the ends of the rack does not well position the inboard ends of the tie rods at the same lateral position as the inboard ends of the front drive pivots, nor does it well position the outboard ends of the tie rods coupled to the wheels by half-shafts. This is also related to the relative position of the suspension arms, which are not aligned ideally with the tie rods. The result is an undesirable angle and configuration of the tie rods, half-shafts, and suspension arms that may further increase stress on the system and that can contribute to reduce handling. Center output steering assemblies exist in the market, but they also suffer from many of the disadvantages noted above. Even with center input and output steering mechanisms, present configurations are quite long and somewhat heavy as a result. This limits design packaging options, vehicle weight, and vehicle weight distribution. This is particularly of concern in side-by-side all-terrain vehicles where rack location is limited by the desired front suspension geometry and chassis width. In addition, it is desirable for the rack to remain protected within the chassis structure. With current steering assemblies, such configuration restrictions result in undesirable steering geometry.
The aforementioned problems with current rack-and-pinion systems typically result in the vehicle and driver experiencing bump-steer when driving on uneven surfaces or on off-road terrain. This can reduce handling while steering the vehicle and can pose risks of failure of the system or safety risks to the riders of the vehicle.
Therefore, a need exists for an improved steering device to obviate the aforementioned problems while providing an improved, light-weight center input and output steering mechanism with a shorter overall length. The present invention provides a compact steering mechanism for vehicles that provides a center rack input and an output member, coupled to a pair of tie rods, and positioned between the ends of the rack while overcoming the deficiencies of existing rack-and-pinion steering systems. The invention therefore provides a compact, light-weight rack-and-pinion steering assembly that has significantly shorter assembly length and weight.